Along with the popularization of computers, various processes for producing lithographic plates have been proposed together with plate material construction. From the aspect of practical use, a process has been generally carried out which comprises preparing a positive or negative film from a block copy and printing out the film on a lithoprinting, original plate. However, a so-called computer-to-plate (CTP) type lithographic material has been developed in which plate-making can be effected by printing the image information edited and prepared directly on a plate material by means of a laser or thermal head. The printed image information is edited and prepared by an electrophotographic plate or silver salt photographic plate for direct plate-making from a block copy without going through a positive or negative film, or by means of electronic composing or DTP (desktop publishment) without converting the information to a visual image. In particular, the CTP type lithographic material makes it possible to rationalize and shorten the plate-making process and to save material costs, so that it is greatly expected that it will find use in the fields of newspaper production in which CTS has been accomplished, commercial printing in which the prepress step has been digitized, and the like.
CTP type lithographic materials have been known which are of the photosensitive type, heat-sensitive type and the type where plate-making is achieved using electrical energy.
When using plate materials of a photosensitive type or a type in which plate-making is effected with electric energy, the plate price becomes high compared to the conventional PS plates, and the production apparatus therefor becomes oversize and expensive, so that these plate materials and the plate-making process using the same have not been put in practical use. Moreover, there is the problem of disposing of developers as wastes.
Some heat-sensitive type plate materials have been developed for light printing uses including in-house printing. JP-A-63-64,747, JP-A-1-113,290 and the like disclose plate materials in which a heat-meltable resin and a thermoplastic resin dispersed in a heat-sensitive layer provided on a support is melted by thermal printing to change the heated portion from hydrophilic to oleophilic. U.S. Pat. No. 4,034,183 and U.S. Pat. No. 4,063,949 disclose plate materials in which a hydrophilic polymer provided on a support is irradiated with a laser to remove the hydrophilic group, thereby converting it to oleophilic polymer. However, these plate materials have problems in that the heat-meltable material present on the support accepts an ink so as to contaminate the non-image area, the plate wear is insufficient, and the freedom of plate material design is restricted.
JP-A-3-108,588 and JP-A-5-8,575 disclose a plate material wherein a heat-sensitive recording layer consisting of a microencapsulated heat-meltable material and a bonding resin is provided on a support and the heated portion is converted to oleophilic. However, these plate materials are not satisfactory in plate wear because the image formed from the microencapsulated heat-meltable material is fragile. On the other than, JP-A-62-164,596 and JP-A-62-164,049 disclose a lithoprinting, original plate in which a recording layer consisting of an active hydrogen-containing binder polymer and a blocked isocyanate is provided on a support having a hydrophilic surface and a process for producing the same. However, this plate material requires a developing step for removing the non-printing portion after printing.
Moreover, one of the direct type lithoprinting materials is a direct drawing type lithoprinting material on which an image area is formed on the surface of a hydrophilic layer by an external means such as ink jet, a toner transcription or the like. JP-A-62-1,587 discloses a plate material for forming a toner-accepting layer by thermal printing which material is coated with a microencapsulated, non-reactive, heat-meltable material. However, this plate material can be used as a printing plate only after an oleophilic toner or the like is fixed on the toner-accepting layer formed, and not such that an image area is formed after the printing.
As mentioned above, a conventional, heat-sensitive, lithoprinting material is poor in plate wear or oleophilicity, so that the use thereof is limited to light printing and the like. Furthermore, some plate materials require a developing step in the plate-making process.
Therefore, JP-A-07-01,849 and JP-A-07-01,850 describe plate materials in the form of reactive microcapsules, which are converted to an image by heat, and which are dispersed in a three-dimensionally cross-linked hydrophilic binder. These plate materials have advantages in that since they are direct plate materials of thermal mode and near infrared laser is used as a source for energy to be applied, they can be handled in an ordinary room and the plate-making process can be greatly simplified because development is unnecessary. However, these plate materials have drawbacks in that (1) particularly when scores of thousands of copies are printed, the plate wear of image area and non-image area are low and (2) since curing by double bond is utilized as a means for strengthening the hydrophilic layer, the amount of double bond-containing groups which are oleophilic must be increased in the hydrophilic layer for strengthening and it is difficult to maintain an adequate balance between the strengthening of the hydrophilic layer and the development of non-imaging property.
As mentioned above, the prior art has a problem in respect of practice on a commercial level with regard to plate performance, plate-making apparatus, plate-making workability or the cost of plate material, plate-making or apparatus. In addition, it has a problem in that the direct lithographic plate which does not require development and which utilizes reactive microcapsules and a hydrophilic binder polymer is also low in plate wear in the image areas and the non-image areas in the case of printing large numbers of copies and it is difficult to maintain an adequate balance in designing the plate construction.
This invention aims at solving the above-mentioned problems of the prior direct type offset plate materials. That is to say, an object of this invention is to provide a lithoprinting, original plate at a low price from which a lithoprinting plate having a high plate wear and a high dimension accuracy is obtained and a contaminant-free printed matter having a clear image is obtained. Furthermore, it is another object of this invention to provide a lithoprinting, original plate which does not require a developing step which in turn requires disposal of developer wastes or the like and can be subjected to plate-making without using special-purpose, large-scale and expensive plate-making apparatus and to provide a plate-making process.